綠屋頂生命週期與成本效益評估

Abstract

綠屋頂因具有延長屋頂壽命、降低建築能耗、減少雨水逕流、空氣淨化、降低熱島效應等多重效益，故已在一些國家推廣，唯傳統式綠屋頂由於較重、安裝費時、不易維護屋頂、影響夜間散熱等問題，故不易在台灣推廣，本研究群因而開發了中空式綠屋頂，唯尚未針對此一種新型綠屋頂作生命週期及成本效益評估，故本研究用針對薄層綠屋頂(GR) 、水盆式中空綠屋頂(HGR)、傳統綠屋頂(CR)三種不同屋頂形式進行綜合評估，且據以比較分析其個人及城市規模成本效益。 本研究所採用的方法主要分為生命週期評估、個人及城市規模成本效益評估等三大部分，生命週期評估主要針對三種屋頂分析及比較其生命週期中對於環境的衝擊，GR及HGR溫室氣體衝擊分別約為4.6、12.1 kg CO2 eq/m2，減碳效益則分別約為30.2及22.8 kg CO2 eq/m2；CR10、GR+CR40及HGR + CR40三種屋頂四十年生命週期的年均成本分別為202、240及229NT$/m2/yr，雖接近但仍比CR20高。若將經濟效益列入考量則GR與HGR分別約為192、183 NT$/m2/yr，已略低於CR10，但仍高於CR15及CR20。 城市規模成本為個人成本資料乘以新竹市可安裝綠屋頂面積而得，GR及HGR的減碳效益分別為10.9及10.5-10.6 kg eCO2/m2/yr；減少排水系統負荷分別為0.276及0.469元/ m2/yr、減少空氣污染物處理及損害成本分別為0.152及0.525元/m2/yr、減少熱島效應則為51.71元/ m2/yr。全市減碳總效益則約分別為164及158-160千噸eCO2 /yr；經濟效益則約109及107-109千萬元/yr，主是來自於節能效益，由於台灣缺乏自有能源，這是很重要的效益，所得結果預期可作為台灣地區綠屋頂相關規劃與決策時之重要依據。

Green roofs (GRs) offer various benefits such as extending roof lifespan and reducing building energy consumption, runoff, air pollutants, and urban heat island effect. However, conventional GRs have several disadvantages including heavy weight, tedious construction, maintenance difficulty, and affecting heat dissipation at night. A new hollow green roof (HGR) is thus developed in this research group, but its life cycle assessment (LCA) and cost-benefit analysis are so far not available. Therefore, this study implements a comprehensive analysis for comparing the life cycle personal and city-wide costs and benefits of the conventional roof (CR), GR, and HGR. This study applied a LCA software to assess the environmental impacts of the roofs and developed a method for assessing the personal and city-wide costs and benefits of the GR and HGR. The materials used by GR and HGR can pose GHG emission impacts of 4.6 and 12.1 kg CO2eq/m2, respectively. However, they can also reduce 30.2 and 22.8 kg CO2eq/m2, while compared with the bare CR. The annual costs of CR10 (CR with a ten-year lifespan), GR+CR40 and HGR+CR40 are 202、240 and 229 NT$/m2/yr, respectively. The costs of the two green roofs, although quite close, are still higher than that of the CR10. The economic benefits of the GR and HGR are about 192 and 183 NT$/m2/yr, respectively. With the economic benefits, the costs of GR and HGR are lower than the cost of CR10, but still higher than those of CR15 and CR20. The city-wide costs and benefits are estimated based on the unit costs and benefits multiplied by the area that can install GRs. The unit (city-wide) carbon emission reduction for the GR and HGR are 10.9 kg (158 kiloton) and 10.5-10.6 kg (160 kiloton) CO2eq/m2/yr, respectively. The drainage system expansion cost reduction are about 0.276 and 0.469 NT$/m2/yr. The air pollutant removal benefits are about 0.152 and 0.525 $NT/m2/yr. And the benefit from reducing heat island effect is about 51.71 $NT/m2/yr. The GR and HGR city-wide economic benefits are NT$10.9 and NT$10.7-10.9 billion/yr, respectively. The economic benefits are mainly contributed by energy savings and are important for this country with very few domestic energy sources. The results are expected to facilitate related GR development planning and decision making.